Add compilerLocation to Compiler datatype

[fendor]

Avoids compiler program lookup logic code in ShowBuildInfo.

Split off from #7498 based on the comment #7498 (comment)

[fendor]

cc @DanielG

[DanielG]

My gut feeling is that this is a bad idea. If you insist on going this way you should replace all the use sites of lookupProgram ghcProgram and similar with this mechanism instead and see if it still makes sense.

[fendor]

I do not insist, I thought it might be a smooth solution, but if it isn't, I feel free to abandon it again

[DanielG]

I didn't mean to imply I don't think it's worth pursuing, I just think just adding this hardly tells us if this is a good idea or not. In my mind the ProgramDB is there for a reason and I'm not sure if moving some of the info it hast elsewhere wont lead to more problems than it solves. Showing how this would replace a lot of error prone (hehe) code would certainly make a stronger case for this approach.

[fendor]

I don't think a single invocation of requireProgram or lookupProgram can be saved, as other data is usually required than just the program location. E.g. to invoke a program, you still need its ConfiguredProgram.

We rarely go the way: Compiler -> ConfiguredProgram -> ProgramLocation

[fendor]

This is probably not very good, so closed